The invention generally relates to polishing pads with a window, systems containing such polishing pads, and processes for making and using such polishing pads.
The process of fabricating modem semiconductor integrated circuits (IC) often involves forming various material layers and structures over previously formed layers and structures. However, the underlying features can leave the top surface topography of an in-process substrate highly irregular, with bumps, areas of unequal elevation, troughs, trenches, and/or other surface irregularities. These irregularities can cause problems in the photolithographic process. Consequently, it can be desirable to effect some type of planarization of the substrate.
One method for achieving semiconductor substrate planarization or topography removal is chemical mechanical polishing (CMP). A conventional chemical mechanical polishing (CMP) process involves pressing a substrate against a rotating polishing pad in the presence of a slurry, such as an abrasive slurry.
In general, it is desirable to detect when the desired surface planarity or layer thickness has been reached and/or when an underlying layer has been exposed in order to determine whether to stop polishing. Several techniques have been developed for the in situ detection of endpoints during the CMP process. For example, an optical monitoring system for in situ measuring of uniformity of a layer on a substrate during polishing of the layer has been employed. The optical monitoring system can include a light source that directs a light beam toward the substrate during polishing, a detector that measures light reflected from the substrate, and a computer that analyzes a signal from the detector and calculates whether the endpoint has been detected. In some CMP systems, the light beam is directed toward the substrate through a window in the polishing pad. A layer of slurry is typically present between the substrate and an upper surface of the window.
In general, the invention relates to polishing pads with a window, systems containing such polishing pads, and processes that use such polishing pads.
In one aspect, the invention features a polishing pad that includes a polishing layer having a polishing surface, and a solid window of material in the polishing layer. The window material has a surface energy of about 40 mJ/m2 or less.
In another aspect, the invention features a polishing pad that includes a polishing layer having a polishing surface, and a solid window of material in the polishing layer. The window material is a fluorinated polymer.
In a further aspect, the invention features a polishing pad that includes a polishing layer having a polishing surface, and a solid window of material in the polishing layer. The window material has an index of refraction of about 1.45 or less.
In one aspect, the invention features a polishing pad that includes a backing layer having an opening, and a polishing layer having an opening aligned with the opening in the backing layer. The polishing pad also includes a solid window of a material in the opening of the polishing layer, a layer of a first adhesive material between the backing layer and the solid window, and a layer of a second adhesive material between the backing layer and the solid window. The second adhesive material is different from the first adhesive material.
In another aspect, the invention features a polishing pad that includes a backing layer having an opening, and a polishing layer having an opening aligned with the opening in the backing layer. The polishing pad also includes a solid window of a first material in the opening of the polishing layer, and a layer of an adhesive material between the backing layer and the window. The adhesive material can be, for example, a polyolefin polymer or an acrylate polymer.
In a further aspect, the invention features a method of constructing a polishing pad. The method includes inserting first and second substantially coextensive layers of adhesive material in an opening in a polishing pad, and adhering a window of solid material to a surface of the first layer of adhesive material.
In one aspect, the invention features a method of constructing a polishing pad that includes adhering a window of a solid material to a first layer of adhesive material, the first layer of adhesive material being adhered to a layer of a second adhesive material different from the first adhesive material, thereby forming an article. The method also includes inserting the article in an opening in a polishing layer having a polishing surface.
In another aspect, the invention features a method of constructing a polishing pad that includes modifying a surface of a transparent article by a method selected from the group consisting of corona treatment, flame treatment and fluorine gas treatment, and securing the article in an opening in a polishing layer having a polishing surface.
Embodiments can include one or more of the following features.
The polishing pad can further include a backing layer supporting the polishing layer.
The window material can have a surface energy of about 30 mJ/m2 or less (e.g., about 20 mJ/m2 or less).
The window material can be a perfluorinated polymer (e.g., a polytetrafluoroethylene).
The window material can have an index of refraction of about 1.4 or less (e.g., an index of refraction that is about the same as water).
The window material can transmit at least about 25% of light impinging thereon at one or more wavelengths of interest (e.g., ultraviolet, infrared, from about 400 nm to about 800 nm, from about 400 nm to about 450 nm, from about 400 nm to about 410 nm, from about 650 nm to about 800 nm).
The first adhesive material can be a polymer, such as an acrylate polymer (e.g., a cyanoacrylate polymer), or a polyolefin polymer.
The first adhesive material can be a primer for acrylate polymers (e.g., a primer for cyanoacrylate polymers).
The first adhesive material can be a double coated film tape.
The polishing pad can be incorporated in an apparatus for polishing a surface of a substrate. The apparatus can further include a platen having a surface on which the polishing pad is disposed, and a polishing head configured to hold the substrate. The polishing head and the polishing pad can be configured so that during operation of the apparatus the surface of the substrate contacts the polishing surface.
In certain embodiments, the window-polishing pad construction can exhibit one or more of the following desirable characteristics: good transmission of energy at the wavlength(s) of interest, good resistance to scratching and/or abrasion during the CMP process, good resistance to fluid (e.g., slurry or water) leakage, and/or relatively low refractive index. In some embodiments, at least two (e.g., all) of these properties are exhibited despite the window being made from a material that generally has relatively low surface energy (e.g., low adhesion to many other materials). This can be particularly advantageous when the material from which the window is made has a relatively low surface energy (e.g., polytetrafluoroethylene) and when the window material has good transmission in the blue range of the visible spectrum (e.g., from about 400 nm to about 450 nm, such as from about 400 nm to about 410 nm), which is desirable when a blue laser or a blue LED is used as the light source.
Features, objects and advantages of the invention are in the description, drawings and claims.